Automated conveyor systems are well known. Automated conveyor systems in current use include synchronous assembly systems, asynchronous or non-synchronous assembly systems and machine tool loading systems.
In a synchronous assembly system, a workpiece proceeds through each stage of the assembly process and does not proceed to the next stage until the remaining workpieces are ready to proceed to the next stage (i.e. each workpiece is in synch with the other workpieces). In synchronous assembly systems, the stage or task that takes the greatest amount of time will limit the rate at which all other tasks or stages can be completed because the other workpieces on the conveyor do not proceed to the next stage until all workpieces, including the workpiece at the slowest stage, are ready to proceed to the next stage.
In asynchronous assembly systems, each assembly task is performed by physically removing the workpiece from the conveyor, performing the task and returning the workpiece to the conveyor where the workpiece is transported to the next stage. The conveyor in asynchronous assembly systems is always moving. However, workpieces are removed from the carrier so that slower tasks or stages do not necessarily slow down the optimum velocity of the conveyor.
In the assembly of any multiple component part, some tasks take longer than others. If one task takes longer than the remaining steps, the longer step will limit the rate of production. To alleviate this problem, many systems include divide sections whereby the longer task is performed in multiple to keep at least one part with the longer task completed moving down the conveyor at all times.
In robotic systems, the preferred asynchronous assembly system includes a carrier for transporting the workpiece through the assembly system. When the carrier and workpiece reach an assembly point, a robotic arm or other mechanism lifts the carrier and workpiece above the conveyor system allowing the conveyor to proceed forward without the carrier and workpiece. If the task to be completed includes the application of a significant amount of force or pressure to the workpiece, it is often been necessary to have the robotic arm move the carrier and workpiece away from the conveyor. This movement requires time and additional hardware to accomplish. Thus, there is a need for a stop assembly, or work stop assembly, that will grasp the carrier, efficiently lift the carrier above the conveyor system and enable the assembly task to be performed to the workpiece directly above the conveyor system. Such a combination stop assembly and carrier system must provide support for the workpiece in all three planes, or the X, Y and Z planes.
In addition to robotic machines performing more assembly functions, there is a movement toward automatic testing or gauging of workpieces as they are assembled or machined. Typically, a workpiece may be tested after every two or three assembly tasks are performed. After a workpiece is been determined to be defective, it must be removed from the assembly line or re-routed to a re-testing station or a repair station. Physically removing the carrier and workpiece from the conveyor system can be costly and time consuming.
A better system would be to flag or otherwise mark the carrier in such a way so to indicate to stop assemblies downstream that the workpiece is defective and no task should be performed. Thus, there also is a need for an improved combination carrier and stop assembly system that enables the carrier to be marked as one carrying a defective workpiece so that stop assemblies downstream from where the defect is detected do not waste time by performing additional assembly tasks (or processing or machining) on a defective workpiece. The "flagged" carrier may then be rerouted at the appropriate place downstream.
Another problem not addressed by the prior art is the 90.degree. turning requirements of many assembly lines. Linked conveyors or transport systems that can turn at 90.degree. angles are known. However, many carrier units that rest on top of the moving conveyor cannot turn at 90.degree. angles with short radiuses without getting jammed in the side walls of the conveyor support structure. Often, special tracks or special conveyor systems must be designed specifically for the 90.degree. turns thereby adding to the cost of the entire assembly system. Thus, there is a need for a narrow carrier unit that will ride on top of a linked conveyor and that will further proceed through a 90.degree. turn with a short radius without undue interference with the side walls of the conveyor system.
Yet another problem not addressed by the prior art is the tendency of carriers to get stuck or hung up at work stop assemblies. Specifically, if the work stop assembly includes a grasping and lifting mechanism for holding the carrier above the conveyor while the task is performed, the carrier can get stuck or hung up on the grasping mechanism. If the carrier is unable to leave the work stop assembly, succeeding carriers will not be able to enter the work stop assembly and the continuity of the manufacturing process will be interrupted.